Origins of Selected Geodetic Datums

This information is presented for its historical interest and is not validated for official use. For a list of the latest validated datum transformation parameters and information about WGS 84, go to NGA Publications on Geospatial Sciences. In particular, you may wish to compare the table below with TM8358.1 Table 1 Geodetic Datums Used in Map Production Page 1 and Page 2 .

The earth is not a sphere, but an ellipsoid of revolution, flattened slightly at the poles and bulging somewhat at the Equator. The ellipsoid is used as a surface of reference for the mathematical reduction of geodetic surveys.

A geodetic datum is the set of defining parameters (including the dimensions of the ellipsoid) which forms the basis for the computation of geodetic positions from horizontal control surveys.

The table below contains the origins of selected datums. See the footnotes that follow for additional information.

Origins of Selected Geodetic Datums

Numbers in parenthesis refer to the footnotes that follow the table.

Datum

Area

Name of Point

Latitude

Xi

Longitude

Eta

Ellipsoid

North American 1927

North America

Meades Ranch

39 13 26.686 N

-1.32

98 32 30.506 W

1.93

Clarke 1866

Old Hawaiian

Hawaii

Oahu West Base Astro

21 18 13.89 N

0.00

157 50 55.79 W

0.00

Clarke 1866

Qornog

Greenland

Station 7008

64 31 06.27 N

0.00

51 12 24.86 W

0.00

International

Hjorsey 1955

Iceland

Hjorsey

64 31 29.260 N

0.00

22 22 05.840 W

0.00

International

Provisional South American 1956

Venezuela, Ecuador, Peru, Bolivia, Chile

La Canoa

08 34 17.17 N

2.42

63 51 34.88 W

-0.55

International

Corrego Alegre

Brazil

Corrego Alegre

19 50 15.14 S

0.00

48 57 42.75 W

0.00

International

Chua Astro

Paraguay

Chua Astro

19 45 41.16 S

0.00

48 06 07.56 W

0.00

International

Campo Inchauspe

Argentina

Campo Inchauspe

35 58 16.56 S

0.00

62 10 12.03 W

0.00

International

Yacare

Uruguay

Yacare

30 35 53.68 S

0.00

57 25 01.30 W

0.00

International

European

Europe

Potsdam, Helmertturm

52 22 51.446 N

3.36

13 03 58.741 E

1.78

International

Odnance Survey of Great Britain 1936

Great Britain: Northern Ireland

Royal Greenwich Observatory, Herstmonceux

50 51 55.271 N

-1.14

00 20 45.882 E

-2.2

Airy

Ireland 1965

Ireland

Royal Greenwich, Herstmonceux

50 51 55.271 N

-1.14

00 20 45.882 E

-2.2

Modified Airy (8)

Merchich

Morocco

Merchich

33 26 59.672 N

0.00

07 33 27.295 W

0.00

Clarke 1880 (2)

Voirol

Algeria

Voirol Observatory

36 45 07.9 N

0.00

03 02 49.45 E

0.00

Clarke 1880 (2)

Adindan

Sudan

Adindan

22 10 07.110 N

2.38

31 29 21.608 E

-2.51

Clarke 1880 (2)

Sierra Leone 1960

Sierra Leone

D.O.S. Astro SLX2

08 27 17.6 N

0.00

12 49 40.2 W

0.00

Clarke 1880 (2)

Liberia 1964

Liberia

Robertsfield Astro

06 13 53.02 N

0.00

10 21 35.44 W

0.00

Clarke 1880 (2)

Ghana

Ghana

GCS Pillar 547 Accra

05 32 43.30 N

0.00

00 11 52.30 W

0.00

War Office (3)

Nigeria

Nigeria

Minna

09 39 08.87 N

0.00

06 30 58.76 E

0.00

Clarke 1880 (2)

Arc 1950

Africa (South of Equator)

Buffelsfontein

33 59 32.00 S

3.46

25 30 44.622 E

-0.88

Clarke 1880 (2)

Tananarive (Antananarivo) Obsy 1925

Malagasy Rep.

Tananarive (Antananarivo Obsy)

18 55 02.10 S

0.00

47 33 06.75 E

0.00

International

World Geodetic System 1972

Sino-Soviet Bloc

World Geodetic System 1972

Herat North

Afghanistan

Herat North Astro

34 23 09.08 N

0.00

64 10 58.94 E

0.00

International

Indian

India, Pakistan, Burma, Thailand, Southeast Asia

Kalianpur Hill

24 07 11.26 N

0.31

77 39 17.57 E

0.00

Everest (5)

Tokyo

Japan

Tokyo Obsy

35 39 17.515 N

0.00

139 44 40.502 E

0.00

Bessel

Hu-Tzu-Shan

Taiwan

Hu-Tzu-Shan

23 58 32.340 N

0.00

120 58 25.975 E

0.00

International

Luzon

Philippines

Balanacan

13 33 41.000 N

3.47

121 52 03.000 E

(9)

Clarke 1866

Kertau

West Malaysia

Kertau

03 27 50.71 N

3.47

102 37 24.55 E

-10.90

Modified Everest (6)

Timbalai

East Malaysia

Timbalai

05 17 03.548 N

0.00

115 10 56.409 E

0.00

Everest

Djakarta

Indonesia (Sumatra, Java)

Butavia

06 07 39.522 S

0.00

106 48 27.79 E

0.00

Bessel

Bukit Rirnpah

Indonesia (Bangka)

Bukit Rimpah

02 00 40.16 S

0.00

105 51 39.76 E

0.00

Bessel

G. Serindung

Kalimantan

Ep. A

01 06 10.60 N

0.00

105 00 59.82 E

0.00

Bessel

G. Segara

Indonesia (Kalimantan, East)

G. Segara (P5)

00 32 12.83 S

0.00

117 08 48.47 E

0.00

Bessel

Montiong Lowe

Indonesia (Sulawesi)

Montiong Lowe (PI)

05 08 41.42 S

0.00

119 24 14.94 E

Bessel

Australian Geodetic

Australia

Johnston Memorial Cairn

25 56 54.5515S

7.68

133 12 30.0771E

-4.19

Australian National (7)

Geodetic Datum 1949

New Zealand

Papatahi Trig Station

41 19 08.900 S

-1.30

175 02 51.000 E

(9)

International

Guam 1963

Marianas Islands

Tagcha

13 22 38.490 N

-10.35

144 45 51.560 E

24.12

Clarke 1866

Local Astrol

World Geodetic System 1972

Camp Area Astro

Antarctica

Camp Area Astro

77 50 52.521 S

0.00

166 40 13.753 E

0.00

International

Note: This table contains historic data that may not meet current standards.

Footnotes for Origins of Selected Geometric Datums

Subscripts A and G refer to Astronomic and Geodetic values respectively. Latitude is reckoned positive northward and longitude is reckoned positive eastward.

The dimensions of the Clarke 1880 spheroid adopted by different countries vary in accordance with which of Clarke's original dimensions are used: (a, b) or (a, f) or which foot-meter relationship is used to convert the units from feet to meters. In the area referenced to Arc 1950 datum, the dimensions adopted are:

Semimajor axis = a = 6 378 249.145 ... meters

Semiminor axis = b = 6 356 514.966 ... meters

The above figures yield:

Flattening = f = 1/293.46 63076 ...

In the areas of Merchich and Voirol datum, the dimensions adopted are:

a = 6 378 249.2 meters

b = 6 356 515.0 meters

the above figures yield:

f = 1/293.46 60208

The latter are the values adopted for construction of Department of the Army Universal Transverse Mercator and latitude function tables.

Dimensions of the War Office Spheroid are:

a = 6 378 300.58 meters

f = 1/296

The World Geodetic System 1972 (WGS 72)is not referenced to a single datum point. It represents an ellipsoid whose placement, orientation, and dimensions best fits the Earth's equipotential surface which, on the average, coincides with the geoid. The system was developed from a worldwide distribution of terrestrial and geodetic satellite observations. The dimensions of the WGS 72 ellipsoid are:

a = 6 378 135 meters

f = 1/298.26

The dimensions of the Everest Spheroid are:

a = 6 377 276.345 meters

f = 1/300.8017

The dimensions of the Modified Everest Spheroid are:

a = 6 377 304.063 meters

f = 1/300.8017

This spheroid has the same flattening as the Everest Spheroid, but a slightly larger axis (28 meters) because of the difference between foot-meter relationship used in Malaysia and the one used in India.

The dimensions of the Australian Spheroid are:

a = 6 378 160 meters

f = 1/298.25

The dimensions of the Modified Airy Spheroid are as follows:

a = 6 377 340.189 International meters

b = 6 356 034.448 International meters

the above figures yield:

f = 1/299.325

Prime vertical deflection is unknown.

Local Astros are several independently determined datum origins for surveys over small areas.

A geodetic datum is defined by five parameters:

Geodetic latitude (Ø0) at the origin

Geodetic longitude (Lambda0) at the origin

Geoid height (N0 at the origin

Dimensions of the Ellipsoid (2 parameters)

An initial geodetic azimuth at the origin may be defined rather than the longitude, but since the Laplace azimuth equation must be satisfied, there is no need to define both. In each of the datums listed, the geoid height at the origin is zero, except for Australia Geodetic Datum where it is 4.9 meters.